PubMed Health⌕ Search

Biomedical subjects

J F Mead

Publications and source records attributed to J F Mead.

At least 37 records · Page 2Linked to original sources
PubMed1981

Thyroid control over biomembranes: VI. Lipids in liver mitochondria and microsomes of hypothyroid rats.

The lipids of liver mitochondria prepared from normal rats and from rats made hypothyroid by thyroidectomy and injection with 131 INa contained similar amounts, per mg protein, of total lipids, phospholipids, neutral lipids and lipid phosphorus. Hypothyroidism caused a doubling of the relative amounts of mitochondrial cardiolipins (CL; to 20.5% of the phospholipid P) and an accompanying trend (although statistically not significant) toward decreased amounts of both phosphatidylcholines (PC) and phosphatidylserines (PS), with phosphatidylethanolamines (PE) remaining unchanged. The pattern of elevated 18:2 fatty acyl content and depleted 20:4 acyl groups of the mitochondrial phospholipids of hypothyroid preparations was reflected to varying degrees in the resolved phospholipids, with PC showing greater degrees of abnormality than PE, and CL showing none. Hypothyroidism produced the same abnormal pattern of fatty acyl distributions in liver microsomal total lipids as was found in the mitochondria. Hypothyroid rats, when killed 6 hr after injection of [1-14C] labeled linoleate, showed the following abnormalities: the liver incorporated less label into lipids, and converted 18:2 not exclusively to 20:4 (as normals do) but instead incorporated the label mainly into saturated fatty acids. These data, together with the known decrease in beta-oxidation, suggest that hypothyroidism involves possible defective step(s) in the conversion of 18:2 to 20:4.

Animals↗
PubMed1981

Metabolism of epoxidized phosphatidylcholine by phospholipase A2 and epoxide hydrolase.

The isolation and measurement of phospholipid epoxides as major peroxidation products in biomembrane preparations prompted an investigation of enzymatic mechanisms which may be responsible for their elimination. Analysis of microsomal epoxide hydrolase and phospholipase A2 activity against a phospholipid epoxide commonly encountered in tissues indicated it to be a poor substrate for epoxide hydrolase, but rapidly hydrolyzed by phospholipase A2. Microsomal and purified phospholipase A2 preparations hydrolyzed the phospholipid epoxide at rates 2-fold greater than were observed with a monoenoic phospholipid from which the epoxide would be derived. The product fatty acid epoxide, cis-9,10-epoxystearic acid, was rapidly hydrated by microsomal and cytosolic epoxide hydrolase. On the basis of earlier reports demonstrating increased phospholipase activity against oxidized phospholipids, and on the results of the present study, a model for the metabolism of oxidized membrane phospholipids is proposed.

Animals↗
PubMed1981

On the mechanisms of fatty acid transformations in membranes.

Concentrations of albumin in excess of 1% in the incubation mixture inhibited the elongation of added fatty acids and their incorporation into microsomal lipids whereas these reactions were not inhibited with endogenous microsomal membrane fatty acids. The results of these and other studies support the idea that such reactions of membrane lipid fatty acids with membrane-bound enzymes normally occur entirely within the membrane without release of free fatty acids to equilibrate with the fatty acid pool during the process.

Albumins↗
PubMed1981

Metabolism of fatty acids in rat brain microsomal membranes.

Using a technique in which substrate fatty acids are incorporated into microsomal membranes followed by comparison of their rates of desaturation with those of exogenous added fatty acids, it has been found that the desaturation rate may be greater for the membrane-bound substrate than for the added fatty acid. Moreover, the product of the membrane-bound substrate is incorporated into membrane phospholipid whereas the product of the exogenous substrate is found in di- and triacylglycerols and in free fatty acids, as well. These and other findings point to a normal sequence of reaction of membrane lipids with membrane-bounds substrates involving transfer of fatty acid from phospholipid to the coupled enzyme systems without facile equilibration with the free fatty acid pool.

Animals↗
PubMed1980

Lipid epoxide hydrolase in rat lung preparations.

The activity of rat lung epoxide hydrolase (epoxide hydrolase, EC 3.3.2.3) was studied using two lipid epoxides which can be isolated from lung tissue. These epoxides displayed different Km,app and hydration rates. Methyl cis-9,10-epoxystearate was hydrated 20-times more rapidly than cholest-5 alpha,6 alpha-epoxy-3 beta-ol. The Km for the lung microsomal enzyme was variable and dependent on the microsome concentration in the medium. A soluble epoxide hydrolase was also detected in both lung and liver. This enzyme appears similar to the microsomal enzyme in its activity toward methyl epoxystearate. The measured activities for liver microsomal epoxide hydrolase were over 8-times those for lung microsomes; activity against cholesterol epoxide was 40-times greater for liver. In spite of the slow rates measured with cholesterol epoxide in lung preparations, this compound was an effective competitive inhibitor against methyl epoxystearate over a wide concentration range. This suggests that cholesterol epoxide readily binds to epoxide hydrolase and is an effective competitive inhibitor against a much more actively metabolized substrate, methyl epoxystearate. Such circumstances indicate that cholesterol epoxide binds with a high degree of nonproductivity to lung microsomal epoxide hydrolase. This attribute of lung epoxide hydrolase may relate to the relatively high concentrations of cholesterol epoxide found in lung tissue.

Animals↗
PubMed1980

A lipid mobilizing factor in serum of tumor-bearing mice.

There is considerable evidence that the growing tumor requires a source of unsaturated fatty acids, but the nature of this source and the mechanism of mobilizing the fatty acids from it are obscure. These experiments make use of AKR mice with implanted adipose tissue labeled with 1-14C linoleic acid. With this experimental animal, it has been found that: (a) in the normal, fed mouse, fat is mobilized slowly and appears largely as respiratory CO2, following oxidation, (b) in the normal, fasted mouse, fat is mobilized rapidly and appears largely as respiratory CO2; (c) in the tumor-bearing, fed mouse, fat is mobilized rapidly and appears largely in the tumor; and (d) the serum from tumor-bearing mice, when injected into normal mice, produces an immediate massive fat mobilization that does not respond to feeding, whereas the serum from normal, fed mice does not. It is concluded that a mobilizing factor of unknown nature is present in the serum of tumor-bearing AKR mice.

Adipose Tissue↗
PubMed1979

Epoxides as products of lipid autoxidation in rat lungs.

The nature and content of lipid epoxides in rat lung were examined in air-breathing control rats and those exposed to nitrogen dioxide. Exposure to 6.5 ppm NO2 for 24 hr resulted in significantly greater epoxide content in a number of lipid classes. It is proposed that lipid autoxidation in lung tissues may contribute to the levels of epoxide-containing lipids. Furthermore, the processes involved in epoxide formation may be predicted from autoxidation studies utilizing a system of unsaturated fatty acid monolayers on silica gel which serves as a model for biomembranes. The findings indicate that exposure to oxidizing gases can lead to an accumulation of lipid epoxides in both lung parenchymal tissue and on the alveolar surface.

Animals↗
PubMed1978

Liver and thymus lipid composition in AKR mice with and without lymphomas.

Lipid composition of liver and thymus in controls, early stage lymphoma, and advanced stage lymphoma-bearing AKR mice was studied. There was a significant decrease in the liver total lipid content in mice with advanced lymphoma, whereas in the early stages, no quantitative change was seen. In livers of mice with advanced stage lymphoma, there was a significant decrease in the nonpolar fraction. The decrease was in triglyceride, whereas the cholesterol fractions were relatively increased though hig,ly variable. There was an increase in the polar lipid/nonpolar lipid ratio in the advanced lymphoma livers and a very large increase in the polar lipid/triglyceride ratio, indicating that the decrease in total lipid in these livers was largely in the triglyceride fraction. Similar changes were seen in the thymus, in which the lipid composition reflected the transformation from normal to malignant cells.

Animals↗
PubMed1977

Autoxidation of fatty acid monolayers adsorbed on silica gel: I. Nature of adsorption sites.

An unsaturated fatty acid monolayer deposited on a silica gel surface has been chosen as a model for studying non-enzymatic autoxidation of membrane lipids. Studies to determine the suitability of this system as a model for biomembranes were conducted to define the nature of the monolayers, particularly with respect to the factors determining the concentration of the fatty acid molecule on unit area of the surface. The results from adsorption isotherm, high temperature dehydroxylation, and infrared spectra studies show that adsorption of a monomolecular layer of fatty acids occurs and that the number of molecules absorbed corresponds to the number of isolated, non-hydrogen-bonded silanol groups. It is presumed the binding is by hydrogen bonding of the carboxyl groups to silanol groups. The packing density of the fatty acid molecules is 1.25 molecule/100 A2 which is similar to the density of the isolated silanol sites on the surface.

Adsorption↗
PubMed1977

Autoxidation of fatty acid monolayers adsorbed on silica gel: II. Rates and products.

Unsaturated fatty acid monolayers on silica gel have been autoxidized, and the rate of fatty acid disappearance and products obtained from those membrane-like assemblies have been studied. Fatty acid monolayers consisting of pure linoleic acid, linolelaidic acid, and oleic acid were autoxidized at 60 C. The rates of autoxidation of linoleic acid and linolelaidic acid monolayers followed by the disappearance of substrates are considerably faster than that in bulk phase, and the rates conform to apparent first order kinetics. Autoxidation of linoleic and linolelaidic acid monolayers, unlike bulk phase, produced only a small amount of diene conjugation, and the major products formed were identified as 9,10-epoxy and 12,13-epoxyoctadecenoic acid in roughly equal quantities. The epoxidation is stereospecific, with cis and trans olefins giving cis and trans epoxides, respectively. Oleic acid was autoxidized to only a small extent during 27 hr and produced no detectable amount of epoxide.

Adsorption↗
PubMed1977

A biochemical concept of cellular production of paramyxoviruses.

Previous analysis in vitro of the interaction between some paramyxoviruses and the chicken embryo has indicated that the cell most productive (MP) of virus is the heart cell whereas the liver cell is least productive (LP). More superior production of virus results from more efficient release of virions, whereas the kinetics of viral attachment and penetration and the production of interferon are similar for both types of cell. Since plasma membrane lipids may represent the structural key to enveloping and release of paramyxovirions, the lipid composition of MP and LP cells and purified plasma membranes was investigated. The plasma membranes of heart cells contain a high molar ratio of cholesterol to phospholipid (1.66 vs. 0.55), more phosphatidylethanolamine (34.8% vs. 24.0% of total phospholipid), and less phosphatidylcholine (39.7% vs. 55.0% of total phospholipid) than the plasma membranes of liver ce-ls. The fatty acids of heart and liver cellular plasma membranes are similar. The glycosphingolipid components of heart and liver cells are also the same, as is the content of gangliosides (6.18 mug vs. 6.49 mug neuraminic acid/mg protein) in these cells, but the heart cell contains one-fifth as much total cerebroside (34.3 mg vs. 174.3 mug cerebroside/mg protein), indicating a greater ganglioside to neutral glycolipid ratio for the heart cell. Comparison of these data with the monkey/hamster (MP/LP) renal cell-parainfluenza SV5 virus system of Klenk and Choppin suggests that essential molecular determinants of superior cellular production of paramyxoviruses are the relative concentration of phosphatidylethanolamine and the molar ratio of cholesterol to phospholipid in the plasma membrane.

Animals↗
PubMed1976

Lipid composition of myelin in multiple sclerosis.

Myelin was isolated from histologically normal white matter and plaques from MS patients and from white matter of neurologically normal controls. No difference was found in the total lipid content. There were no detectable deficits in MS myelin of phosphoglycerides, plasmalogens or sphingolipids. Gangliosides and lysolecithin were not detected. Analysis of the fatty aldehyde composition of the phosphoglycerides and the fatty acid composition of the cholesteryl esters, phosphoglycerides and sphingolipids did not show any differences between the normal and MS myelin.

Cerebrosides↗
PubMed1976

In vitro activity of the fatty acyl desaturases of human cancerous and noncancerous tissues.

The microsomal desaturase activity of human cancerous and noncancerous tissues was measured in vitro using 1-14C, -11, 14-eicosadienoic and 1-14C-oliec acids as substrates. Tissues used were a case of ovarian cancer, a urinary bladder cancer, a rectal cancer, and a non-specific colonic ulcer with appropriately normal tissues. When 11, 14-20:2 was used as substrate, radioactive tetraene and triene were produced. The tetraene was identified by radio gas chromatography as arachidonic acid (5, 8, 11, 14-20:4), and the triene had a retention time of 5, 11, 14-20:3. Thus, the possibility arises that a delta8 desaturase was involved. In the delta6 desaturase, with the urinary bladder cancerous tissue, the desaturase activity appeared to be decreased in comparison to neighboring tissue, whereas with the colonic cancer tissue, the desaturase appeared to be relatively increased, though the number of samples was inadequate for confidence.

Adult↗